Diagnostic imaging occupies an important position in the field of ophthalmology. In recent years, utilization of optical coherence tomography (OCT) has advanced. OCT is being used not only for acquiring B mode images and three-dimensional images of a subject's eye but also for acquiring front images such as C mode images and shadowgrams. In addition, acquiring an image that emphasizes a specific site of the subject's eye, and acquiring functional information are also performed.
For example, OCT angiography, which forms an image in which retinal blood vessels and choroidal blood vessels are emphasized, is attracting attention (for example, refer to Japanese Translation of PCT International Application Publication No. 2015-515894). In OCT angiography, the same site of the fundus (e.g., the same cross sections) is scanned multiple times. In general, the tissue (i.e. structure) of the scanned site is invariant in time, but the blood flow portion inside the blood vessel changes with time. In OCT angiography, an image is formed by emphasizing a portion where such temporal change exists (i.e., emphasizing blood flow signals). By performing such iterative scanning and signal processing on a plurality of cross sections, a three-dimensional distribution of fundus blood vessels is obtained.
However, in OCT angiography, if fixation displacement occurs during multiple scans of the same site of the fundus of the subject's eye, the portion where the deviation occurs is emphasized as a portion where the above temporal change exists, and hence the portion is depicted as an artifact extending linearly in the scanning direction. It is difficult to completely remove this type of noise even with tracking that moves the OCT optical system or controls the scanning position according to the movement of the subject's eye.
In addition, in the image obtained in the manner as described above, the blood vessel regions and the artifact regions are emphasized. Therefore, the artifact regions are also included in the analysis target in the image, which lowers the reliability of the analysis result.